1. Field of the Invention
The present invention relates to a muffler having resonance chambers, more particularly, it relates to a muffler able to suppress a plurality of frequencies.
2. Description of the Related Art
Mufflers are widely utilized in many fields; in particular, a muffler having a resonance chamber for reducing noise produced in the intake and exhaust systems of a combustion engine is well known.
FIG. 14 shows a conventional muffler, wherein the muffler comprises two casing elements 1 and 2, and a T-shape connecting pipe 3. The casing element 1 is integrally constructed of a cup-shaped portion 1a and a pipe portion 1b extending through a bottom 1c of the cup-shaped portion 1a, and the casing element 2 is integrally constructed of a cup-shaped portion 2a and a pipe portion 2b extending through a bottom 2c of the cup-shaped portion 2a. The casing elements 1 and 2 are made from a synthetic resin, by monolithic molding.
The connecting pipe 3 comprises a communicating portion 3a and connecting portions 3b and 3c. The cup-shaped portions 1a and 2a are engaged with each other at the end portions 1d and 2d, and at the same time, the pipe portion 1b is fitted into the connecting portion 3b and the pipe portion 2b is fitted into the connecting portion 3c. The engaging portion 4 of the end portions 1d and 2d is welded.
The above construction defines a shielded resonance chamber 7, and the pipe portions 1b and 2b are communicated with the resonance chamber 7 through the communicating portion 3a.
In this kind of muffler, the noise frequency suppressed by the muffler is mainly determined by the volume of the resonance chamber 7 and the diameter and length of the communicating portion 3a.
In this conventional muffler, only one noise frequency can be suppressed, but recent developments have created a demand for the suppression of low frequency noise. Namely, in many cases, the suppression of only a single noise frequency is not sufficient to meet the requirements for a much lower level of noise.